Thermo-mechanical fatigue investigation of single crystal nickel base superalloy SRR99

This paper deals with the comparison between thermal fatigue (TF) and thermomechanical fatigue (TMF) testing for SRR99 superalloy. First, a measured TF mechanical strain-temperature (e m -T) profile between 200°C and 1100°C has been reproduced on a TMF specimen to allow for an estimation of the stresses and inelastic strains which occur during TF. Thermal-fatigue-based (TFB) e m -T profiles were determined based on the measured TF profiles. These TFB cycles, together with the well-known out-of-phase profile, were employed for all of TMF tests. The comparison of the results reveals that the TF and TMF out-phase tests are more damaging in terms both of the applied stress and strain range, while the TMF out-of-phase test is more severe if the comparison is made in terms of the inelastic strain range. Finally, it is shown that the results can be rationalized quite well by plotting the fatigue lives as a function of the maximum stabilized stress (σ m a x ).